Data threatening to break physics

What should a rational scientist do with an impossible result?

Antonio Eredato insists that the interview with him was conducted on Skype, and that both cameras were included. This is a man slightly older than middle-age, with gray hair framing wide-open eyes and a chiselled chin. He smiles easily, and his eyes catch the eye, like a searchlight. Italian accent adds extra vowels at the end of the words he utters.

We talk 15 minutes before he agrees to give an interview under the recording. He says that he does not want to encourage journalists who can distort his words and give a sensational and unreliable story. He agreed to talk with me on Skype because I am not a journalist, but a physicist and at the same time an author who has spent 13 years in the trenches of experimental particle physics. In the end, he says: “Well, I looked into your eyes, I trust you. Perhaps this is my problem. I may be too trusting, but I trust you. ” He laughs and leans back in his chair, stretching his arms to the side.

Ereditato is a former leader of 160 physicists from 13 countries that make up the OPERA collaboration, created to study neutrino physics. It was first proposed to be assembled in 2000, and Eredato managed it from 2008 to 2012. Then in the winter of 2011, something impossible seemed to happen. “The person who studied the data calls me,” says Eredato from my computer screen. - He says: "I see something strange here." He saw evidence that neutrinos passed through 730 km of the earth's crust, from Switzerland to Italy - and they should do this - at such a high speed that they arrived at their destination 60.7 ns faster than light could travel such a distance space - which should not be.



Over the past hundred years, Einstein's observations, according to which massive objects cannot move faster than the speed of light in a vacuum, embedded in his special theory of relativity, have become the cornerstone of our understanding of the universe. If the measurements of OPERA were correct, they would have marked the first violation of this theory. It would be an atomic bomb in the heart of our understanding of the universe.

I ask Eredato if he thought that this should be a mistake. “I don’t think it would be fair to say that,” he tells me. - If we say so, we distort our analysis. So when we got a hint of something so amazing, the first reaction was: let's see why this is so. "

Wolfgang Pauli postulated the existence of a neutrino in 1930 to solve a simple problem. When nuclei experience beta decay, emitting an electron or positron, the equivalent of an electron from antimatter, something is missing. Either something invisible is emitted with the electron / positron, or the energy disappears. Since in no reproducible experiment where anything flew, fell, moved, collided, decayed or did not change, no energy disappeared, Pauli proposed a neutrino, an invisible particle, with all the properties necessary to bring about beta decay. in accordance with the first law of thermodynamics. By the invisibility of a particle, I mean that when neutrinos pass through matter, they rarely leave a mark. It is so rare that it took almost 30 years to find physical evidence of their presence in the experiment (conducted by Frederick Raines and Clyde Cowan ).

Today, neutrinos are an integral part of the Periodic Table of the Standard Model in particle physics. Here you will find the particles that make up the matter, listed in pairs and divided into three categories: electron neutrinos are paired with electrons, muon neutrinos - with muons, and tau neutrinos - exactly like that, with tau. Neutrinos can transform from one type to another. For example, an electron neutrino can oscillate into a muon, and a muon can turn into a tau. “ Neutrino oscillations are the first signs of physics outside the Standard Model,” Eredato says to me. He adds with a laugh: “Because I like neutrinos.”

Which brings us back to the OPERA experiment. With his idea, there was already much evidence of neutrino oscillations, but they all came from experiments with extinction. That is, the evidence was that either the electron or muon neutrino disappeared. Experiments were required with the appearance - this was the goal of OPERA. The idea was that at CERN, the European Organization for Nuclear Research in Geneva, they would create a beam of muon neutrinos aimed at a detector buried deep under the Italian mountain range Gran Sasso d'Italia, 730 km from the source. If tau neutrinos are detected there, then neutrino oscillations will occur. In accordance with the tradition of particle physics experts, to give experiments bright acronyms, the project was called OPERA (Oscillation Project with Emulsion-tRracking Apparatus) [a project of studying oscillations using an emulsion tracking apparatus].

The neutrino velocity measurement from CNGS (CERN Neutrinos to Gran Sasso) [Neutrinos from CERN to Gran Sasso] to the OPERA detector was not mentioned in the proposal. But in February 2011, the OPERA project focused almost entirely on this.


OPERA detector uses thousands of photographic film “bricks”

"I think, like any scientist, I was very, very, very skeptical from the very beginning," says Eredato. “You are making a checklist: timer, receiver, GPS, transmitter from receiver to detector ... Check everything." Some variants of the shallows very quickly, others checked time. The experiments at CERN could not be stopped. Meanwhile, Erredato was hard-hitting his team. " You can’t imagine how I worked at that time with my colleagues - check it, check it, do it, do it, repeat it, repeat it again - we did it from spring till September 23! ”

The team tested and tried all versions of software, hardware, theories that they could think of, every step, every bug fixed, every bit of knowledge gained, evidence that neutrinos moving faster than light stood firmly above the whole experiment. And then the inevitable happened and the news of the data leaked out. People not engaged in the experiment began to spread rumors about the violation of the theory of relativity, a result that would have shaken the fundamentals of physics in the way that they had not been shaken since 1900, when Max Planck discovered quantum physics. Rumors "spread at the speed of light," Eredato tells me.

“What happens next? You decide to take the place of the chapter on public relations. What to say: no comments? But then everyone will accuse you, all journalists will say: “Oh, so you are hiding something. We want to know what's going on. We pay taxes and support you, we have the right to know! "Or you make a statement." In a sinister voice, he says: "I discovered superluminal neutrinos."

In this case, it was not Eredato who decided everything. Large experimental associations like OPERA have instructions for handling controversial results and vote to announce results to the public. Only a few people voted against the announcement. "And I respect them very much, and they were right in the end, which is why they respect them."

OPERA announced the results on September 23, 2011 at a special CERN seminar. The team did not claim to have discovered a violation of the theory of relativity. Instead, phrases like “evidence” or “discovery” were used, and the data was called an “anomaly”. But this key nuance is lost in the sensation of human interaction. And although there was a reservation in the headline published by The New York Times: “Tiny neutrinos may have broken the cosmic speed limit”, it was not in an article in The Daily Telegraph (“Scientists from CERN broke the speed of light record”) or The Guardian (“Scientists say they detect particles moving faster than light”) or Scientific American (“Particles moving faster than light” were found).

The physical community took the news with skepticism, and even cynicism. Not a single practicing professional physicist was ready to abandon the SRT, just as Wolfgang Pauli was not ready to abandon the law of the conservation of energy in 1930. But still, what if? Since the confirmation of the key dogmas of the Standard Model in experiments UA1 and UA2 at CERN in 1983, each discovery in particle physics (except for neutrino oscillations) added one more check mark to this piggy bank of this annoyingly sacred Standard Model. How could particle physics experts resist the temptation to hope that anything, anything, could explode this area even during their lifetime?

Even Ereditato hoped a little. “You come to the podium at a scientific conference, at a seminar, and say: Guys, I have something here that I don’t understand. Please help us understand this. ” He pauses and nods, more to himself than to me. “I think this is a good choice, modesty. And in general, everyone dreamed that we were right. Everything".

In one direction lay an epic breakthrough physics, and in the other a potential shame. Should OPERA have to wait? How many months more could you analyze and reanalyze the result? Leaning towards me pointing at me through the camera, Eredato explains why a scientist cannot ignore a measurement, even if it seems absurd. “This can not be killed. Nature speaks to us not through theories, but through experimental results. The worst data is better than the best theory. If you are looking for reasonable results, you will never make discoveries, or at least you will not make unexpected discoveries. You can commit - conflicting terms - the expected discovery. "

One thing is clear: the announcement provided OPERA with the help she hoped for. A few days later, with the help of the CNGS beam operators, they began to develop a new approach to measurement. In the original analysis, we had to use statistical techniques to determine the arrival time of the neutrino, since the beam diverged. The new approach was to generate neutrinos in dense batches so that they would come to the detector together, making the time of their arrival will be much easier to determine.

It took two months to reconfigure the neutrino beam, perform the experiment and analyze the results - an unprecedentedly fast time for such a complex experiment.

And measuring the speed of light has not gone away. “And then I was scared,” says Eredato. - I said: "Oh, my God." And not only I, many people who were very critical of this, could not say anything in the face of this result. ”


Scientist studies OPERA detector at the Gran Sasso National Laboratory

Experiments in particle physics consist of complex house-sized detectors and particle accelerators. Development and construction begin many years before the first results are obtained. By the time the detector and collider are already working, experimenters are developing software for analyzing and sifting data, and for separating the signal and noise, rare and exotic from the usual and boring music from noise. They use their version of blind analysis, similar to double-blind testing in biomedicine, requiring a “closed signal box”. Instead of checking their equipment on real data, they check them on simulated data, designed to reproduce the response of the detector equipment to known processes. As a result, when they “open the box”, their measurements should not be distorted by some conscious or unconscious desire to make the discovery.

However, the OPERA neutrino data were faster than light. The next step was to receive independent confirmation from a source outside OPERA, as is customary. For example, the Higgs particle was observed in both ATLAS and CMS experiments. But there were no other experiments that could confirm or deny what was happening on OPERA for at least several years. However, on the basis of the Gran Sasso there was another experiment, the Large Volume Detector (LVD), which at least could check the time counting system at OPERA. The idea was to make sure that the clocks of both experiments were synchronized by comparing the time of arrival of cosmic rays from the muons in both detectors.

“It was a really amazing experiment,” Eredato tells me. Looking at the data obtained at OPERA for five years, the researchers found a period in which the time measurement at OPERA worked with a shift of 73 ns. Then another error was detected in the timer, which influenced the experiment with a condensed beam: the clock frequency at OPERA was not synchronized with the frequency of the beams. The combination of these two problems fully compensated for the 60 ns advance that was recorded at the arrival of muon neutrinos with CNGS.

The source of problems with the timer was a fiber optic cable that transmitted time signals from GPS from the Gran Sasso surface to a depth of 8.3 km, where the OPERA detector was located. The cable had two tricky problems: first, it was poorly connected, so that one could expect that the receiver would not perceive signals from it at all. If the receiver sees the light, it must run the neutrino race to the detector. If the receiver does not see the light, there should be no launch. But as a result, everything turned out wrong. Instead, this receiver required about 73 ns to gain enough light energy to trigger neutrinos and activate electronics. As a result, the electronics marked the start of the neutrino 73 ns after they actually left the starting line at CERN. “I could have expected that there was either a signal or not. But there are no signals with a delay, ”says Ereditato. Secondly, the cable connector appears to have been shifted. “The cable was normally plugged in about a week before we started collecting data, and was plugged in normally when we checked everything again,” says Eredato. “The meanness is that between these events, when we collected data on the neutrino velocity, the cable was plugged somehow wrong.”

After finding and correcting the errors of measuring the neutrino velocity at OPERA are the most accurate in the world. And they perfectly fit the Einstein service station. Weak hope for the existence of a new physics, not predicted by a respectable Standard Model, has died. But the work of the OPERA team, which found the only cable left among the thousands of electrical channels of the experimental equipment, was amazing. “I am proud,” Eredato tells me. - To be honest, I have always believed that a solution will be found among strange phenomena. Side effects, such that no one would think. I would never have thought of such a thing as a cable, never. ” And the collaboration also did not exaggerate the data, and did not make unconfirmed statements. They did not make any statements at all, and conducted an investigation in close cooperation with other teams.

However, it was clear that someone was wrong somewhere. Perhaps it was the person who attached the cable, or developed the receiver, or someone else. In March 2012, when the dust had settled, the OPERA collaboration held another vote to determine if the participants are sure of the project leaders. Each organization participating in the project had one vote. Voting ended with a score of 16 to 13 in favor of the expression of distrust, several abstentions were voted. This was far from the required 2/3 of votes to be considered a majority and impeach the leadership, but enough for the message to be heard. The leader of OPERA, Eredato and coordinator of the experiments, Daria Autiero, resigned.

Eredato’s resignation letter clearly stated that he was leaving for the good of the team: “as a result of the huge interest from the media, the OPERA collaboration was under anomalous, and in a sense, changing pressure. And external pressure rather quickly seeps into the social system of 150 people, which leads to potentially dangerous results, to the danger of losing sight of scientific goals. This is too much risk. In order to avoid this risk, the opinions of individuals must be sacrificed. ”

Did Ereditato do something bad? People are wrong. I spent 13 years working on experiments at SLAC, Fermilab, Cornell University, CERN, and even in a long-standing superconducting supercollider . Perhaps I am easier to forgive mistakes than people who have never had to crawl around the server room, connecting and distributing cables. Connectors fail for a bunch of reasons, and if there are thousands of channels, you can safely say that no scientific experiment has taken place without failure of a couple of connectors. Usually they are easy to find, but not this time. Some say that OPERA should have conducted more checks, but by the time the vote of no confidence had passed, a whole year had passed. How many more months did they have to do this? Should their loyalty to the SRT have to force them to wait until the problem is found? No, they would then be led by an absurd concept, according to which scientists must follow a certain scientific credo.

Perhaps the disappointment expressed by the voting results speaks of how strongly scientists, especially experimenters, want to find something new, something unpredictable, and how angry they are when this possibility disappears.

I asked Ereditato to evaluate all the experience I had gained entirely. “Society likes to divide everything into black and white,” he replies.But in science, the answers are not always so clear. “We need to be careful, because if we create the impression that science never says yes or no, always says possible, then people will say well, then science does not need to believe.” The issue of bringing this message is very delicate. ” Most journalists writing about science are not scientists. "They treat scientific information in the same way as murders or abductions." Regarding his role personally? "I learned that we all play our part in this area."

Today, Eredato is director of the Laboratory of High Energy Physics at the University of Bern, and continues to participate in various experiments with neutrinos. The OPERA experiment, meanwhile, continues to hunt for neutrino oscillations and collect tau neutrinos under another direction. While they scored four of them.

Ransom Stevens - physicist, writer, technologist, journalist. His first popular science book, The Left Hemisphere speaks, and the right one laughs: a disrespectful, but accurate description of the neurobiological views on talent, skills, innovations, discoveries, art and science. (but accurate!) look at the neuroscience of talent & skill, innovation & discovery, and art & science] was released in 2015.